A. Bly, H. Woodard, and D. Winther

Introduction

Soybean production is increasing in South Dakota with many different tillage. Row spacing varies from wide (30") to narrow rows(6
7n). Therefore a long
term research project was initiated to evaluate the influence of row spacing, tillage system, and P treatment on three soybean varieties from three maturity groups at Brookings SD.

Materials and Methods

A research site was established in 1995 on the Agronomy farm near Brookings SD. A randomized complete block design with 4 replications, tillage system as the main plot, row spacing as the sub
plot, P treatment as the split plot, and variety as the sub plot was used. No till and conventional tillage systems were established. A chisel plow was used for tillage on the conventional till blocks. Row spacings were 7 and 28 inch. Phosphorus (P) treatments were a check with no added P and a P treatment where P would be non limiting to crop growth. In May of 1995, 50 Ibs/a P2O5 was applied as 10 0 with a spoke applicator set at 8.5 inch spacings and soybeans were planted. In 1996, corn was planted on this site with no P application. Tillage systems were maintained in 1996. Prior to planting soybeans in 1997, 0 6” soil samples were taken from the check and P treated split blocks, tillage systems were maintained as in prior years, and 100 Ibs/a P2O5 was applied to P treated split blocks with same methods as 1995. Hendricks (maturity group 0), Granite (maturity group I), and Sturdy (maturity group II) were planted at 200,000 pure live seeds/a on June 2, 1997. Due to extremely dry soil conditions throughout May and June, it was deemed necessary to irrigate this site in order to get even seedling emergence. On June 16 and 17, 1.66 inches of water was applied with sprinkler irrigation system. Pursuit at 1.44 oz/a and Poast Plus at 8 oz/a was applied on July 1, 1997 for broadleaf, residual, and crabgrass control. Poast Plus at 32 oz/a and Lorsban at 16 oz/a were applied on July 28, 1997 for control of crabgrass and grasshoppers. Early bloom (EB) shoot samples were taken and number of plants counted from a 12.5 ft2 area of each plot on July 29, 1997. EB samples were dried, weighed, and ground for nutrient analysis. Grain was harvested with a small plot combine on October 20, 1997. Grain samples were cleaned, weighed, test weight and moisture were determined. ANOVA of dependent variables was completed using SAS.

Results and Discussion

Soil test results showed that extractable Olsen P of 26 ppm for the P treated blocks and 23 ppm for the check P blocks. P levels for both treatments are considered very high. The ANOVA showed that dry weight/plot, grain test weight and yield were influenced by variety, dry weight/plot, and yield was influenced by row spacing (Table 1). Tillage only influenced grain test weight. There were few interaction terms of significance.

Shoot dry weight (early Bloom stage) was greater for the group 0 variety (Hendricks) than for the other varieties, but this variety was lowest in test weight and grain yield (Table 2).
Shoot dry weight harvested from the 7” rows was greater than for the 28" rows partly because the seeding population was more appropriate for the 7" row spacing than for the wider spacing. Overall grain yields are slightly below the long term average soybean yields. This was due in part because of the moisture stress observed a few times during the growing season. However, grain yield was also higher in the 7" row spacing primarily because the plants in the 28" row spacing were more crowded within each row and competition for resources, especially moisture, was greater in the 28" row spacing. Greater test weight was observed in the Hendricks variety that the other varieties for both tillage systems (Table 3). The grain yield of all varieties pooled for the 7" row spacing was greater in both tillage systems compared to the varieties grown in the 28" row spacing.  Grain yield from conventional tillage was not affected by row spacing, but significantly different under no-till with 7 inch rows significantly higher when compared to 28 inch rows (Table 4).

Conclusions

• When yield potential is low, tillage doesn't seem to influence grain yield.
• Plant row spacing was a factor in increasing grain yield since there was less competition in the narrow spaced rows than in the wider rows.

This project was partially funded by the South Dakota Soybean Research and Promotion Council.
 

Table 2.  Mean early bloom dry matter weight per plot and plant, number of plants per acre, grain test weight and yield by tillage method, soybean variety, row spacing and phosphorus treatment for
the soybean experiment at Brookings SD in 1997. (project no. 17297)

	Dependent Variable
Main	Early Bloom Shoot Dry Weight		Plant	Grain
Effects	per plot	per plant	population	test weight	Yield
	-----------------g-----------------		no./a	lb/bu	bu/a
Variety:
Hendricks (0)	133.4b	2.6	173060b	56.8a	25.7a
Granite (I)	123.3ab	3.3	160237b	57.4b	28.3b
Sturdy (II)	113.3a	3.0	130711a	57.4b	27.9b
LSD(.05)	13.4	NS	15313	0.2	1.3
Row Spacing:
7 inch	152.8	3.3	161710	57.3	28.9
28 inch	93.9	2.6	147629	57.2	25.7
LSD(.05)	30.4	NS	11006	NS	1.4
Tillage Method:
No-Till	120.1	3.1	155316	57.3	26.3
Conventional	126.6	2.9	154023	57.1	28.3
LSD(.05)	NS	NS	NS	0.1	NS
P Treatment:
check	117.0	3.0	155819	57.2	27.0
150 lbs/a P2O5	129.7	3.0	153520	57.2	27.6
LSD(.05)	NS	NS	NS	NS	NS

LSD - Least significant difference test between two means.

Table 3 & 4?????
 
 

Last Updated on 5/27/98
By Howard J. Woodard
Email: woodardh@mg.sdstate.edu

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